1. Field of the Invention
The invention relates to the recovery of phosphate ester values from distillation residues containing amounts of phosphate esters and in particular the phosphate esters from the residue derived from the production of aryl phosphate esters.
2. Related Art
The residue by-product from the distillation of aryl phosphate esters is a viscous, black, odoriferous material having very poor flow properties. A typical residue is comprised of about 84 wt. % phosphate esters, 16 wt. % of other organics (primarily comprised of alkyl diphenyl ethers and alkylated benzenes and free phenolics), condensed phosphates and inorganics. Some of the residue is currently sold commercially under the trademark PHOSFLEX Z. The remainder of the residue is disposed of by drumming or by pumping into storage ponds.
Increasingly, however, due to the escalation of phosphate ester production, the prices of feedstock materials and increasingly stringent waste disposal regulations, new methods of recovering the phosphate esters from the residue have been sought. Such recovery would reduce the manufacturing cost for triaryl phosphates as well as decrease the volume of waste produced.
U.S. Pat. No. 1,994,591 discloses the extraction of triphenyl phosphate or other plasticizers, as listed at Col. 5, lines 9-17, from a solid nitrocellulose or cellulose acetate plastic. The process comprises initially leaching the plastic material containing the plasticizer with a solvent which dissolves both the plasticizer and the nitrocellulose subcoating and thereafter adding water to precipitate some of the nitrocellulose. Thereafter more water is added to precipitate the plasticizer and the remaining nitrocellulose. The filter cake recovered is leached with a low boiling paraffin hydrocarbon to recover the plasticizer from the solid polyhydroxylic nitrocellulose in low purity. A subsequent recrystallization is needed to attain adequate purity of the solid plasticizer.
U.S. Pat. No. 2,217,706 discloses a process similar to that disclosed in U.S. Pat. No. 1,994,591. U.S. Pat. Nos. 2,315,495 and 2,373,807 disclose processes for purifying phosphoric acid esters, such as triaryl or trialkylphosphates, from the dephenolization of waste aqueous liquors by mixing the esters to be purified with finely ground inert substances and dissolving the esters out therefrom by utilizing an aliphatic hydrocarbon.
The cited prior art were directed to the recovery of phosphate esters (generally triphenylphosphate or triaryl or trialkyl phosphates)from either waste plastic residue or from the dephenolization of waste aqueous liquors from coal or oil hydrogenation plants. In the cited art the wastes from which the phosphate esters are removed have a chemical composition which differ substantially from the waste matter being treated in the instant disclosure. For instance, the cited art are directed to recovering phosphate esters from oxygen free contaminants while the waste of the instant process comprise contaminants rich in oxygen-containing compounds.
The object of the invention therefore is to devise a means of recovering phosphate esters from waste residues containing such residues.